The present invention relates to a method and apparatus for drying a substrate such as a semiconductor wafer and a liquid crystal display glass after the substrate has been cleaned.
FIG. 28 illustrates one example of a drying process known in the art. This known process is called the "direct displacement isopropyl alcohol (IPA) drying process", also known as the "Marangoni drying process". A rinsing bath 92 is closed by a lid 91 and filled with pure water 93. After a semiconductor wafer W (hereinafter, simply referred to as a "wafer") has been cleaned by a chemical agent, it is immersed in the pure water 93 for rinsing purposes. A gas mixture of isopropyl alcohol vapor and nitrogen is then fed to the upper interior space of the rinsing bath 92 through gas inlet and outlet ports 95a and 95b to fill the upper interior space with the mixture.
Thereafter, a holder 94 on which the wafer W is placed is raised toward the upper interior space of the rinsing bath 92 as shown by phantom line in FIG. 28. when the wafer W upwardly passes past the level of the pure water, isopropyl alcohol is attached to the surface of the wafer W. A change in the surface tension of water due to concentration gradient of isopropyl alcohol causes a film of water attached to the surface of the wafer to be forced back to the pure water. This enables the surface of the wafer to be quickly dried out. In this example, the holder 94 is raised within the rinsing bath. Alternatively, the pure water 93 may be withdrawn from the rinsing bath 92 whereas the holder 94 is fixed in place.
FIG. 29 illustrates another example of a drying process known in the art. In this example, the holder 94 is fixed in place. A gas mixture of isopropyl alcohol vapor and nitrogen is fed to the upper interior space of the rinsing bath 92 through the gas inlet and outlet ports 95a and 95b. The gas pressure causes the pure water 93 to be displaced from the rinsing bath 92 through a drain valve 96. After the pure water 93 has been withdrawn, heated nitrogen is fed to the rinsing bath through second gas inlet and outlet ports 97a and 97b to thermally dry out the surface of the wafer. In this example, the pure water 93 is withdrawn. The holder 94 may alternatively be lifted.
FIG. 30 illustrates a further example of a drying process known in the art. This known process is called the "hot water drying process". The pure water 93 within the rinsing bath 92 is heated to a predetermined temperature. The wafer W is immersed in the resulting hot water after it has been cleaned by a chemical agent. After the wafer has been rinsed, the holder 94 on which the wafer W is placed is raised to a position shown by phantom line in FIG. 30. The wafer is then dried by air or hot air. In this example, the holder 94 is lifted. The pure water 93 may alternatively be withdrawn from the rinsing bath 92 while the holder 94 may be fixed in place.
All of the known drying processes present the following common problems. As shown in FIG. 31A, the holder 94 includes a pair of support arms 94a. A plurality of Y-shaped wafer holding grooves 94b are formed in the upper ends of the support arms 94a. The wafer W is inserted into the grooves 94b whereby the wafer W is held in a vertical orientation. As shown, on an enlarged scale, in FIG. 32, the wafer W is constantly in contact with a portion of the wafer holding groove 94b.
As shown in FIG. 32, a water droplet 98 remains between the wafer W and the groove 94b when the wafer W is moved out of the pure water, or the pure water is withdrawn from the rinsing bath.
In such a case, a certain period of time is required to dry out the water droplet 98. This results in an increase in the time required to complete the drying process and brings about a reduction in the throughput of the apparatus. Moreover, watermarks are left on the surface of the wafer due to foreign substance contained within the water droplet while the water droplet 98 is being dried. Such watermarks may cause the wafer to malfunction.